1. Field of the Invention
The present invention relates to motion sensors generally and, more particularly, to a novel motion sensors which senses purposeful movement, as opposed to nonpurposeful motion such as vibration, and is especially useful when employed as a sensor in an on-demand power assisted steering system. While the sensor of the present invention is described in an embodiment in which it is so employed, it will be understood that it may be applied as well in any case in which it is desired to sense purposeful motion and, more particularly, in which it is desired to sense a predetermined degree of motion occurring within a predetermined length of time.
2. Background Art
Power assisted steering systems are well known devices for assisting the turning of wheels to effect changes in direction of motion of automobiles, trucks, and a wide range of industrial and construction equipment such as fork lift trucks, for example. A power steering assist unit typically comprises a hydraulic motor operatively connected to the steering shaft of vehicle and powered by an electric motor. In its simplest embodiment, the unit operates whenever the vehicle motor is operating.
In order to conserve energy, power assisted steering units have been developed which are activated only under certain conditions, e.g., when the steering wheel is turned, when the vehicle is moving, or when the vehicle is in a certain speed range. One problem with the first type is that purposeful motion is not discriminated and random movements such as vibration can cause the unit to cycle on and off which, in some cases, represents a large power drain; and, in the case of electric forklift trucks, the drain can exceed the traction motor in terms of peak power. The latter two types have as one disadvantage, among others, that there is no power assist to turn the wheel should a vehicle need to maneuver out of a confined space by turning the wheel when there is no vehicle motion.
Accordingly, it is a principal object of the present invention to provide a motion sensor which can discriminate between purposeful motion and random motion such as vibration.
Another object of the invention is to provide such a motion sensor which can be employed with an on-demand power steering assist unit and which does not require vehicle motion before the unit is activated.
An additional object of the invention is to provide such a sensor which does not require fine adjustments and which can be used in industrial environments.
Other objects of the invention, as well as particular features and advantages thereof, will be elucidated in or apparent from the following description and the accompanying drawing figures.